Photographic stabilising or fixing bath

ABSTRACT

IN THE PRODUCTION OF PHOTOGRAPHIC IMAGES BY THE EXPOSURE AND DEVELOPMENT OF SILVER HALIDE EMULSIONS THE STABILISATION OR FIXING THE EXPOSED AND DEVELOPED EMULSION BY A BATH CONTAINING A MERCAPTOTRIAZINE STABILISER.

United States Patent 3,712,818 PHOTOGRAPHIC STABILISING 0R FIXING BATH Fritz Nittel and Hans Oblschlager, Cologne-Stammheim,

and Kari-Wilhelm Seliranz, @pladen, Germany, assignors to Agta-Gevaert Aktiengesellschaft, Leverkusen, Germany No Drawing. Filed June 25, 1969, Ser. No. 836,661 Claims priority, application Germany, June 27, 1968, P 17 72 734.3 Int. Cl. G03c 5/38 U.S. Cl. 96-61 1 Claim ABSTRACT OF THE DISCLOSURE In the production of photographic images by the exposure and development of silver halide emulsions the stabilisation or fixing of the exposed and developed emulsion by a bath containing a mercaptotriazine stabiliser.

The invention relates to a bath for stabilising or fixing exposed and developed photographic silver halide emulsion layers, which contains mercaptotriazine compounds as stabilising or fixing compounds.

The term stabilisation is intended to mean the conversion of the remaining light sensitive silver halide which is present in an exposed and developed silver halide emulsion layer into a complex silver compound which is not light sensitive. This silver complex may either remain in the layer or may be partly or completely Washed out. Fixing is intended to mean dissolving the light sensitive silver halide out of the developed silver halide emulsion layer. Both methods serve the same purpose, namely to render the layer which carries the final photographic image insensitive to light. However, any transitional stage between these two extreme cases in which either all the light insensitive complex remains in the layer or is completely removed by dissolving out soluble complexes from the layer is possible. This depends mainly on the Water solubility of the complex and on the treatment time in the stabilising bath or on the length of time for which the material is subsequently washed.

Stabilisation of a developed silver halide emulsion layer generally proceeds much more rapidly than conventional fixing, so that this method of working is particularly important for modern high speed processing methods.

Although many stabilising agents are already known, they do not meet all the practical requirements. One of the most serious disadvantages is the gradual discolouration, especially of the white parts of the finished silver image which may become yellow to deep brown. This eifect is due to an insufiicient stability of the silver complex. Free silver ions are formed and these cause the discoloration. Another serious disadvantage is bleaching of the silver image. Other known stabilizing agents such as thiocyanates are strongly hygroscopic. The resulting high moisture content often leads to sticky layers. Other stabilizing agents are not sufficiently effective or can be used only at relatively high pH values which cannot be tolerated in photographic layers. Thiourea and similar compounds are only stable at acid pH values. They are decomposed in alkaline mediums to yield silver sulfide. Many of the heterocyclic mercapto compounds described for this purpose cause fogging of the photographic layer in the developer baths. This is a serious disadvantage since it is almost impossible to avoid contamination of the developer bath with small quantities of the stabilising bath, especially in machine processing.

It is an object of the invention to develop new stabilising agents in which the silver complex has sufficient stability and which can be used over a very wide pH range.

3,712,818 Patented Jan. 23, 1973 A photographic stabilising or fixing bath has now been found which contains a water-soluble triazine compound of the following formula as the stabiliser or fixer:

R"N N-R' N l RI in which R or R is a hydrogen atom, a saturated or unsaturated aliphatic group having up to 6 carbon atoms such as methyl, ethyl propyl, butyl or allyl groups which may be substituted, e.g. with phenyl groups as in the benzyl or phenylethyl radicals or an aryl radical, in particular a phenyl group;

R is a hydrogen atom, a saturated or unsaturated aliphatic group having up to 6 carbon atoms such as methyl, ethyl, butyl or allyl groups, which aliphatic groups may be substituted with hydroxyl, alkoxy, amino halogen or phenyl groups such as hydroxymethyl, 2- hydroxypropyl, 2 -methoxyethy1, '2 aminoethyl, 3-dimethylaminopropyl, 2-chloroethyl or 3-chloropropyl or benzyl group or is an aryl group, in particular a phenyl group.

The solubility of the compounds can be influenced as desired by suitable choice of the substituents R, R and o R" and the compounds can thus be adapted to the par ticular purpose for which they are to be used.

The following are examples of suitablecompounds:

The compounds which are used according to the invention can be prepared by known processes, for example as described by Dixon, J. Chem. Soc. (London) 61, 510, Burke, J. Am. Chem. Soc. 69, 236-237 (1947) or Paquin, Angew. Chem. 60, 267 (194-8). The method of preparation of compounds and 7 is described in detail below.

COMPOUND 5 70 g. of ethanolamine is introduced into a mixture of 76 g. of thiourea and 60 g. of paraformaldehyde in 250 ml. of isopropanol in such a way, with stirring and cooling, that the temperature does not exceed C. The mixture is then heated under reflux for 2 hours, cooled, filtered with suction and washed with isopropanol. Yield 132 g. When recrystallised from methanol, the compound melts at 163-165" C.

COMPOUND 7 160 ml. of a Formalin solution is introduced with stirring to a mixture of 102 g. of 1-amino-3-dimethylamino propane and 76 g. of thiourea in the course of 20 minutes, the temperature rising to 85 C. in the process. The reaction mixture is then heated for 10 minutes at 90 C., and after cooling, suction filtration, Washing with isopropanol and drying, 110 g. of compound 7 of M.P. 145-147" C. are obtained. After recrystallisation from methanol, the substance melts at 148 C.

Tihfl baths according to the invention can be used both as stabilising baths and as fixing baths. Whether they are used for one or the other purpose depends on the watersolubility of the complex compounds formed between the silver halide and the triazine compounds contained in the baths and, of course, on the length of the treatment time of the developed photographic material in the bath and the length of any subsequent washing.

The required fixing times are much shorter than for the conventional sodium thiosulfate fixing baths. If elevated temperatures are employed, as is the case with high speed processing methods, e.g. temperatures of about 50 C., the fixing times are only slightly longer than in ammonium thiosulfate baths. It is also advantageous that the baths prepared according to the invention may have an acid pH as is required e.g. for short stop fixing baths, since the triazine compounds are stable at pH values between 1 and 4. Thiosulfate fixing baths, on the other hand, must not be allowed to have pH values below 4 because decomposition of the thiosulfate then occurs.

The baths according to the invention are particularly advantageous if they are used as stabilising baths, especially in high speed processing methods. The stabilising time is very short, 30 seconds to 3 minutes generally being sulficient. The photographic images which have been stabilised with the baths prepared according to the invention show practically no discoloration even after prolonged storage. The finished silver image is very stable even Without the presence of stabilisers such as phenylmercaptotetrazole which are usually added, and bleaching occurs only to a very small extent even after prolonged storage under tropical conditions.

In contrast to the most commonly used stabilisers, ammonium thiocyanate and sodium thiocyanate, which result in sticky layers, the substances according to the invention in no Way influence the mechanical properties of the layer. In particular, no odours are produced by the baths according to the invention nor are they found in the stabilised photographs.

The baths may have either an acid or an alkaline pH when they are used as stabiliser or fixer baths. In this respect they are far superior to the usual stabiliser baths which contain thiocyanates or thiourea. The stabiliser baths according to the invention should preferably have a slightly acid pH value of about 4 to 6.5.

The triazine compounds contained in the baths according to the invention are photographically inert. Fogging of the photographic layers does not occur even if traces of the compounds enter the developer bath.

The amount of triazine compounds contained in the baths according to the invention may vary within wide limits. Quantities of between 50 and 250 g. per litre are generally suflicient. The optimum concentrations for any particular process can be easily determined by simple small scale tests.

The baths according to the invention are prepared by simply dissolving the triazine compounds in water. A small quantity of a water-soluble solvent such as formamide, dimethylformamide etc. is preferably added to the baths according to the invention. This results in an improvement of the diffusion into the gelatine layers.

The mercaptotriazines are particularly useful in very viscous high speed fixing baths. Such baths are of great importance in modern high speed processing methods. If known fixing agents, such as ammonium thiosulfate are used, it is extremely difiicult to prepare sufficiently viscous fixing baths of a pasty consistency because at the high thiosulfate concentrations required, it is not possible to achieve a sufficiently high viscosity with the thickness customarily employed such as cellulose derivatives, e.g. hydroxyethylcellulose. The fixing baths according to the invention, on the other hand, can be easily adjusted to the required viscosity with the usual thickening agents.

EXAMPLE 1 Commercial photographic black-white materials containing silver bromide gelatine emulsion layers are exposed behind a step wedge and developed in a hydro- ,quinone/p-aminophenol developer. The film samples have the following sensitivities:

Sample I: 27 DIN Sample 2: 21 DIN Sample 3: 17 DIN Sample 4: 13 DIN The films are then stabilised by treating them with a 15% aqueous solution of compound 5 at a pH of 9.5.

A criterion for determining the completeness of stabilisation is, as in the case of fixing, the clarity of the imagefree parts of the developed and treated photographic material. The material to be treated can be stabilised by dipping it in the stabilising baths. It is not necessary, however, to wait until the 'film which is to be stabilised becomes clear in this bath. The films may also be treated for only a relatively short time in the bath and then taken out. The stabilising process then continues even after removal from the bath in the developed silver halide emulsion layer which is soaked with stabilising agent. In the following table, the treatment time in the bath is called the immersion time and the time outside the bath is termed the clarification time. The efiiciency of the baths according to the invention is clear from the following table.

Similar stabilisation times are required for ammonium thiocyanate as the most usual stabilising agent. However, the stabilised photographic pictures produced are unusable because the layers are very sticky.

The layers which have been stabilised according to the invention are completely non-sticky. Tests on the stabilised pictures after being in the heating cupboard (3 days storage at 46 C.) and under tropical conditions (3 days storage at 60 C; and 50% relative humidity) demonstrate the excellent stability of the stabilised pictures. No discolouration or bleaching occurs.

How the whole stabilisation process is divided up into immersion time and clarification time depends on the desired conditions to be employed for processing. Thus short immersion times followed by long clarification times are desirable, for example, in machine processing which has a short entry path for the stabilising bath and longer outflow parts for the final drying.

EXAMPLE 2 A commercial photographic black-white material con taining a silver iodobromide gelatine emulsion layer is exposed, and two exposed samples are then processed with the following fixing developer's (monobath-processing).

Fixing developer I: G. Hydroquinone 35 l-phenyl-pyrazolidone 7 Sodium sulfite 25 Sodium hydroxide 20 Sodium thiosulfate 150 Made up to 1 litre with water. Fixing developer II:

6 The fixing developer was adjusted to pH 12.8 with NaOH.

The exposed film samples are treated with the above baths for one minute at 20 C. The sample strip treated with bath 1 remains cloudy; it is insufiiciently fixed.

The strip treated with bath 2 has been completely fixed. The parts which are free from image are completely clear.

It, will be seen from the above comparison that sodium thiosulfate as fixing agent in fixing developers is much less sensitive than bath 2 which is prepared according to the invention. Corresponding tests with other mercaptotriazines to be used according to the invention yield similar results.

EXAMPLE 3 15 g. of hydroquinone and 7.5 g. of formaldehyde sodium bisulfite are added to 1 kg. of a photographic emulsion which contains 120 g. of gelatine and 0.24 mol of AgCl. The emulsion is applied on baryta paper.

Since the above material already contains the developer in the light sensitive layer, only an alkaline activator bath is required for development. The photographic material is exposed behind a grey step wedge in a conventional sensitometer and worked up as follows:

An automatic apparatus is used. The rate of processing can be so adjusted that a photographic sheet measuring 30 x 40 cm. takes 60 to seconds to run through the apparatus. If compound 5 in the stabilising bath is replaced by equivalent quantities of other mercapto triazines of dthe above table, the stabilisation times are of the same or er.

If ammonium thiocyanate is used as stabilising agent, similar lengths of time are required. The pictures obtained, however, are unusable owing to their stickiness, especially if materials with a hydrophobic support are used. If other stabilising agents such as thiourea are used instead of the stabilising agents according to the invention, the final picture becomes bleached or discoloured. Suitable tests on photographic. images after storage in the heating cupboard and tropical cupboard show that those which have been processed with the baths according to the invention show excellent stability.

The stabilizer baths according to the invention are completely harmless physiologically. They are not found to have any unpleasant odour.

Similar results are obtained if the final bath is omitted and an acid short stop bath at pH 2 is used after the activator. This is especially advantageous in cases where the supports have not been rendered hydrophobic.

EXAMPLE 4 Samples of the photographic film types described in Example 1 are exposed and developed in a similar manner. However, the samples are not stabilised but fixed. The treatment differs from that described in Example 1 in that the developed film samples are left in the fixing bath until the image-free areas are clear. The optical clarity of these areas is a criterion for the fact that the light sensitive silver halides have been quantitatively dissolved out by the fixing process. The film samples are processed in the following baths:

Bath 1: G. Sodium thiosulfate cryst. 160 Potassium metabisulfite 15 Up to 1000 ml. pH 4.6.

Bath 2: 15% aqueous solution of ammonium thiosulfate,

Bath 3: 10% aqueous solution of compound 1, pH 9.8

Bath 4: 10% aqueous solution of compound 5, pH 9.5

Bath 5: 110% aqueous solution of compound 5; adjusted to pH 4.1 by the addition of acetic acid Bath 6: 10% aqueous solution of compound 1; adjusted to pH 1.1 by the addition of phosphoric acid The results of the tests are summarised in the following table.

TABLE 1 Fixing at 20 0., clarification times in seconds Sensitivity of film, DIN

The excellent effect of the fixing agents according to the invention compared with a conventional acid fixing bath (Bath 1 with sodium thiosulfate) can be clearly seen.

Although Bath 2 is superior to the bath according to the invention in the clarification times, it has the disadvantage for practical purposes of having to be followed by a very long washing to remove excess ammonium thiosulphate quantitatively from the processed layer. This is necessary in the case of ammonium thiosulfate in order to prevent yellowing and bleaching of the finished image. The triazine derivatives used in accordance with the invention do not have this disadvantage so that a short washing is suflicient.

What is claimed is:

1. The photographic process of producing a photographic image in a silver halide emulsion layer, developing and fixing the exposed emulsion, the step of treating the developed emulsion in a stabilising or fixing bath having a pH in the range from 4 to 6.5 consisting essentially of an aqueous solution of an agent of the following formula:

in which R, or R is a hydrogen atom, or a saturated or unsaturated aliphatic group having up to 6 carbon atoms or a phenyl group; R" is an aliphatic group having up to 6 carbon atoms which is substituted with hydroxy, alkoxy, amino, halogen, a CI-I CH 2-thiohexahydro-s-triazinyl group, treating the developed emulsion in the absence of sufficient thiocyanate ions or thiosulfate ions to provide stabilisation, said agent being present in the bath in an amount ranging from 50 g. to 250 g. per liter of the bath whereupon the exposed light-sensitive silver halide is stabilised or removed.

References Cited UNITED STATES PATENTS 2,476,536 7/1949 Dersch 96--109 2,819,965 1/1958 Murray 96-109 2,948,612 8/1960 De Angelus 96-109 3,239,340 3/1966 Nasu 9661 3,335,009 8/1967 Rasch 96--61 3,364,032 1/1968 Jones 96-140 3,367,780 2/1968 Fix et a1. 96-122 FOREIGN PATENTS 1,335,294 7/1963 France.

I. TRAVIS BROWN, Primary Examiner M. F. KELLEY, Assistant Examiner 

